Modulator circuit



July 25, 1950 J. R. MOORE 2,516,135

MODULATOR CIRCUIT Filed July 22, 1943 OSCILLATOR INVENTOR. JAMES R. MOORE Z/MM Q ATTORNEK Patented July 25, 1950 MODULATOR CIRCUIT James R. Moore, DutehNeckNeJ:

Application Jilly 22; 1943; Serial No. 495,718

(Granted-under... the act of March. 3, 1883,,as

.amended.April 30,- 1928; 370-0..G,1l57) '7 Claims.

Theinventiondescribed herein-may be manu-- factured and used by or for'the Government forgovernmental purposes, without the. payment-to me; of any royalty thereon.

T his invention:- relates ;to: electron-tube modulatingmetworks, particularly the application of such networks .for pulse: modulating the :transa mitter' of pulse-echowobject detection equipment.

Thea-tubes of: such transmitters are usually maintainedtatcutoff "by a -high negative bias impressed rupon the grids or: insufiicient potential on the plates-. Sharp positive pulsesofhigh peak powerg developed *in'; a modulator; are :impressed onzsaidEli-ds, to overcome said bias; orqonsaid plates:- toxraise. their; potential, so that the trans-' mitter oscillates for the duration. of saidpulses. Such oscillating periods are of relativelyishort durationseparated; by: intervals of :considerably longer duration.

Itais :an object of thisinvention to provide an improved modulator for: thewabovementioned purpose; More particularly; it .isaniobject ofthe invention toxprovidexa modulator :which con: sumes a substantial amount of-poweronlywhile the transmitter .is beingwapulsed- Thispermits development ofihigh peakrpower while the: average 'powerrzdissipated is maintainedatza relatively low rlevel.

For this purposev a. portioni of w the. impedance in the output circu-iflofthe modulator-tubecon sists' of an electronic impedance .whiclizis varied simultaneously with, and in opposite sense: as, theaimpedance of the. modulator tube.

Forv-a'sbetter understanding of the invention, together: with other and further; objectszthereof, reference is "hadito the following description taken ini connection with the, accompanying. drawing, and-its scope will bezpointed outin the accompanying claims.

Referring to the drawing, which shows: a schematic circuit of.:=my invention; tubes Ii] and. l 2t are part of, a conventional transmitter oscillator,..the.-;usua1; plate potential sources. and tuning .andcoupling elements {b eing omitted. Said tubes are normally blocked by means of anegative': potential. impressed upon the grids thereof from a-potential source [3; through-a high re.-; sistance I 4: Said .tubesi areadaptedto beinter. mittentlyunblocked by means :of sharp. positive pulses of voltage impressed upon the gridsain such direction as -to overcome said'negativebias; so that the oscillatorfunctions'. for: the: duration of said pulses;

The: pulses arederived from the. output-circuit ct lav modulator. networhcomprisin tWo-tubes-J-E and I6 having theirespace -current.paths.- cone.

nected in series with I a resistor; l land .-a :source of highipotentialiB voltage l8: Tube l6;is--also. connected to a secondsourcerofiB voltagedflin series Witha diode Zll and resistor ll. Source 49 is .of' considerably lower voltage-than source l-B.

A-high'value resistance-22 is shunted across the.

grid and cathode of tube-l6; Terminal 23 adaptedto be connected to .2. sources of intermittentl -y generated. negative goingpulses -.ofl

short? duration, spacedat I intervals of considerably longer duration.

The-above described circuit operates :as fol lows: Since there is no grid bias impressed..on--

tubal-8; said-tube. is normally conductingrand a current ,flows'from source It, through diode. '20,.

resistor l'l;-the anoder-cathode 'path of time s l 6, and-then back: to the source. through ground.

The voltage. drop. vacross resistor I 1 biases: the.

grid: of tube .15 negativelywith respect to its.

cathode :sothat said. tuberoperates :at or .below platecurrent cutoffsand no current can flowthere-through' from'source l 8. Under these. iCOIlP; ditions .tube l5rconstitutes, in effect, a loadof.

substantially infiniteimpedance in the anode.

circuit oftubelfi, sothat no DOWGIriS dissipated from source. I8;

The grid oftube l 6 -is intermittentlyrendered negative by means-of sharpnegativeegoing pulses, impressed thereonfrom.terminal 23, throughra blocking-- condenser; 24, of lowim'15e dance-to-=the pulse components. Each negative-goingpulseblocks tube 16 *so that-the current through re.- sistor. I 'l reduced. to -zero. The --blocking bias on: the grid of tube I5 is therefore removed and the impedanceof' said: tube-is suddenly reduced to a relatively low value.

This causes -:the 'potential at th .cathodebf tube IE to rise to substantially-the potentialboi the anode of said tube and a suddensurgeof current takesplaceirom source l8, through tube |5,*,b10cking condenserZl, of low impedance to. the pulse voltage, and resistance ML-tdground.

The direction .of this current is such as to ,bias

between pulses, even though tube I6 is conducting. Resistor I1 is of the order of a few hundred ohms and the voltage of source I9 is small compared to the voltage of source l8, so that the power dissipated between pulse intervals is relatively low compared to the peak power developed in the circuit.

There has been described a pulse modulator network including a normally conducting tube and an electronic impedance in the plate circuit of said tube. Between pulse intervals said tube is conducting but the electronic impedance is kept substantially infinite by means of a cutofi bias voltage developed across a relatively small resistance in the conducting channel including said tube. When a sharp negative voltage is impressed on the grid of said tube, it is rendered non-conducting and the electronic impedance is at the same time reduced to a minimum thereby causing a tremendous reduction in the voltage drop thereacross. The resulting voltage is impressed in such direction on the grid circuit of the oscillator as to overcom the blocking bias thereon and permit it to generate sustained oscillations for the duration of said pulse.

If plate modulation is used, then the output of the modulator will obviously be applied to the plates of the oscillator.

The modulator network has thus far been described as applied to suppressed carrier pulse,

modulation. It is, however, equally applicable to continuous carrier modulation systems using other types of modulation signals, e. g. sinusoidal waves.

For'this purpose, the negative grid bias on the oscillator tubes Ill and I2 is reduced to permit said tubes to oscillate continuously. Both modulator tubes l5 and i6 are normally maintained conducting by reducing the negative bias applied from resistor I! to the grid of tube l5 so that said bias is insufiicient to maintain said grid at plate current cutoff. This can be done connecting the lead from the grid of tube l 5 to an intermediate point of resistor l1, rather than to the lower end thereof. Another way of accomplishing this result is to reduce the value of resistor [1, or to reduce the current therethrough by decreasing the voltage of source i9, or to apply a negative bias to the grid of tube IE, or by a combination of the above expedients.

'While there has been described what is at present considered a preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims, to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. An electronic network comprising a pair of electron tubes having their space current paths connected in series with a source of potential, means to maintain one of said tubes conducting, means responsive to said conduction to bias the other tube to cutofi, and means responsive to a signal to render said one of said tubes non-conducting, so as to remove said cutoff bias and render said other tube conducting, whereby the relative potential drops across said tubes are altered, and an output circuit coupled to the junction of said space current paths.

2. An electron relay comprising at least first and second grid controlled electron tubes, a source of plate potential having its positive pole connected to the anode of said first tube, and its negative pole connected to the cathode of said second tube, the cathode of said first tube being connected to the anode of said second tube, a signal input circuit for said relay connected between the grid and cathode of said second tube, a load circuit coupled to the junction of said anode and cathode, means to normally maintain said second tube conducting and said first tube non-conducting, said means including a second source of potential between the anode and cathode of said second tube, and means responsive to changes in input voltage to reverse the conducting states of said tube whereby the potential of said junction is altered.

3. An electron tube network comprising first and second electron tubes each having at least an anode, cathode and grid, an impedance having one end connected to the cathode of said first electron tube and having its other end connected to the anode of said second electron tube and the grid of said first tube, means to posi tively bias the anodes of said electron tubes with respect to their cathodes, means including a second source of plate potential to maintain said second tube normally conducting whereby a current flows through said impedance and said second tube, and whereby the resulting voltage drop across said impedance maintains the grid of said first tube negatively biased with respect to its cathode, and means to impress signals upon the grid of said second tube to decrease the conductivity of said second tube, whereby the drop across said impedance is decreased and the conductivity of said first tube is increased, and a load circuit responsive to said increase in conductivity. I

4. An electron tube network comprising first and second electron tubes each having at least an anode, cathode and grid, an impedance having one end connected to the cathode of said first electron tube and having its other end connected to the anode of said second electron tube and the grid of said first tube, a source of plate potential connected between the anode of said first tube and the cathode of said second tube, means including a second source of plate potential to maintain said second tube normally conducting, whereby a current fiows through said impedance and said second tube, and whereby the resulting voltage drop across said impedance maintains the grid of said first tube sufficiently negative to render it non-conducting, and means responsive to signals to render said second tube momentarily non-conducting, whereby the drop across said impedance is decreased, said first tube is rendered conducting and the positive potential of its cathode is increased, and means responsive to said increase in cathode potential.

5. An electron tube network comprising a diode, first and second electron tubes each having at least an anode, cathode and grid, a resistor having one end connected to the cathodes of said diode and said first electron tube and its other end connected to the anode of said second electron tube and the grid of said first tube, means to positively bias the anodes of said diode and said first electron tube with respect to the cathode of said second tube, said second tube being normally conducting whereby a current flows through said diode, said resistor, and said second tube, and whereby the resulting voltage drop across said resistor maintains the grid of said first tube sufficiently negative to render it nonconducting, and means to render said second tube momentarily non-conducting, whereby the drop across said resistor is decreased, said first tube is rendered conducting, and the positive potential of its cathode is increased, and a load circuit responsive to said increase in cathode potential.

6. A network as set forth in claim 5, wherein said load circuit is connected across said diode.

'7. A network as set forth in claim 5, wherein said load circuit is connected in series with a blocking condenser across said diode.

JAMES R. MOORE.

REFERENCES CITED The following references are of record in the file of this patent:

Number 1 1 Number 6 UNITED STATES PATENTS Name Date Kotowski Nov. 28, 1939 Wilson Nov. 12, 1940 Wilson Nov. 12, 1940 White Apr. 28, 1942 Clough July '7, 1942 Lindquist Sept. 15, 1942 FOREIGN PATENTS Country Date Great Britain Nov. 6, 1933 

